# Salmonella enterica as a Complementary Model to LPS for Immune Stress in Weaned Piglets: Systemic and Intestinal Alterations

## TL;DR

This study compares Salmonella infection and LPS in piglets, showing Salmonella causes more severe gut damage and systemic inflammation, making it a better model for immune stress.

## Contribution

The study introduces an optimized Salmonella enterica infection model that better mimics natural infection effects compared to LPS in weaned piglets.

## Key findings

- Salmonella infection caused more severe and sustained systemic inflammation and gut structural damage than LPS.
- Oral administration of 2 × 109 CFU Salmonella enterica for 24 h created a reproducible and physiologically relevant immune stress model.
- Salmonella infection led to villus perforations and mitochondrial damage not observed with LPS.

## Abstract

The post-weaning period is a critical transition phase in pig production, during which piglets exhibit increased susceptibility to enteric pathogens and associated intestinal disorders. To investigate the underlying mechanisms, lipopolysaccharide (LPS), a component of bacterial cell walls, is frequently used to induce immune stress in experimental models. However, LPS administration alone fails to recapitulate the full spectrum of pathological changes caused by live bacterial infections. In this study, we established an oral infection model using Salmonella enterica (SE), a major enteric pathogen, and systematically compared its effects with those of LPS in weaned piglets. Our results demonstrated that while both challenges in duced immune activation and intestinal injury, SE infection provoked more severe and sustained systemic inflammation, along with distinctive gut structural damage, such as villus perforations and mitochondrial damage, that were not observed in the LPS group. Notably, an oral dose of 2 × 109 CFU SE for 24 h established a reproducible and physiologically relevant model that closely mimics natural Salmonella infection. This optimized model provides a valuable experimental platform for further research on intestinal diseases and for evaluating nutritional or therapeutic interventions aimed at enhancing gut health in swine, with potential benefits for animal welfare and sustainable pork production.

Lipopolysaccharide (LPS) is widely used to model immune stress in weaned piglets, but it does not fully replicate the pathophysiological alterations induced by live bacterial infection. This study therefore established an oral Salmonella enterica (SE) challenge model and systematically compared its effects with those of LPS to evaluate its potential as a complementary immune stress paradigm. Forty piglets were assigned to five groups: control (saline), LPS (intraperitoneal, 100 μg/kg BW), and three SE groups receiving low-, middle-, or high-dose oral SE (1 × 108 CFU/mL, 2 × 108 CFU/mL, or 3 × 108 CFU/mL in a 10 mL saline volume, respectively). Both LPS and SE significantly reduced average daily gain, while only SE challenge decreased colon length. A transient rectal temperature elevation occurred at 8 h in all challenged groups, persisting at 12 h in the LPS and high-dose SE groups. Serum cytokine analysis revealed that LPS induced early but transient interleukin-12 and tumor necrosis factor-α elevation at 8 h, followed by sustained suppression of interferon-γ, interleukin-6, and interleukin-8. In contrast, the middle-dose SE triggered robust increases in multiple pro-inflammatory cytokines at 24 h. Both challenges significantly reduced the CD4+/CD8+ T cell ratios in blood and lymphoid organs and decreased intestinal interleukin-10 levels. SE infection produced more severe intestinal pathology, including dose-dependent villus perforations, microvillus disorganization, and mitochondrial cristae vacuolization, beyond the villus shortening and goblet cell reduction observed in both groups. While both LPS and SE induced immune stress and intestinal injury, SE infection caused more severe and comprehensive pathophysiological alterations. Oral administration of 2 × 109 CFU SE for 24 h established a physiologically relevant immune stress model that effectively mimics natural Salmonella infection in weaned piglets, providing a valuable tool for studying enteric diseases and evaluating interventions.